Unit Library CMake Reference

There are a few CMake variables that control the build process, they can be altered to change how the units library is built and what exactly is built.

CMake variables

  • BUILD_TESTING : Generate CMake Variable controlling whether to build the tests or not

  • UNITS_ENABLE_TESTS : Does the same thing as BUILD_TESTING

  • UNITS_BUILD_STATIC_LIBRARY: Controls whether a static library should be built or not

  • UNITS_BUILD_SHARED_LIBRARY: Controls whether to build a shared library or not, only one or none of UNITS_BUILD_STATIC_LIBRARY and UNITS_BUILD_SHARED_LIBRARY can be enabled at one time.

  • BUILD_SHARED_LIBS: Controls the defaults for the previous two options, overriding them takes precedence

  • UNITS_BUILD_FUZZ_TARGETS: If set to ON, the library will try to compile the fuzzing targets for clang libFuzzer

  • UNITS_BUILD_WEB_SERVER: If set to ON, build a webserver, This uses boost::beast and requires boost 1.70 or greater to build it also requires CMake 3.12 or greater

  • UNITS_BUILD_CONVERTER_APP: enables building a simple command line converter application that can convert units from the command line

  • UNITS_ENABLE_EXTRA_COMPILER_WARNINGS: Turn on bunch of extra compiler warnings, on by default

  • UNITS_ENABLE_ERROR_ON_WARNINGS: Mostly useful in some testing contexts but will turn on Werror so any normal warnings generate an error.

  • CMAKE_CXX_STANDARD: Compile with a particular C++ standard, valid values are 11, 14, 17, 20, and likely 23 though that isn’t broadly supported. Will set to 14 by default if not otherwise specified

  • UNITS_BINARY_ONLY_INSTALL: Just install shared libraries and executables, no headers or static libs or packaging information

  • UNITS_CLANG_TIDY: Enable the clang tidy tests as part of the build

  • UNITS_CLANG_TIDY_OPTIONS: options that get passed to clang tidy when enabled

  • UNITS_BASE_TYPE: Set to uint64_t for expanded base-unit power support. This increases the size of a unit by 4 Bytes.

  • UNITS_DOMAIN: Specify a default domain to use for string conversions. Can be either a name from the domains namespace such as domains::surveying or one of ‘COOKING’, ‘ASTRONOMY’, ‘NUCLEAR’, ‘SURVEYING’, ‘USE_CUSTOMARY’, ‘CLIMATE’, or ‘UCUM’.

  • UNITS_DEFAULT_MATCH_FLAGS: Specify an integer value for the default match flags to be used for conversion

  • UNITS_DISABLE_NON_ENGLISH_UNITS: the library includes a number of non-english units that can be converted from strings, these can be disabled by setting UNITS_DISABLE_NON_ENGLISH_UNITS to ON or setting the definition in the C++ code.

  • UNITS_DISABLE_EXTRA_UNIT_STANDARDS: If set to ON disables UN recommendation 12, X12(not implemented yet), DOD(not implemented yet), from being included in the compilation and generated from strings.

  • UNITS_NAMESPACE: The top level namespace of the library, defaults to units. When compiling with C++17 (or higher), this can be set to, e.g., mynamespace::units to avoid name clashes with other libraries defining units.

  • UNITS_INSTALL: This is set to ON normally but defaults to OFF if used as a subproject. This controls whether anything gets installed by the install target.

  • UNITS_CMAKE_PROJECT_NAME: This is set to UNITS by default. If using this in a package manager or wish to rename the project this variable can be set to another name to change the name of the package. This will change the install path and cmake target names. For example setting -DUNITS_CMAKE_PROJECT_NAME=LLNL-UNITS will create cmake project llnl-units::units, and llnl-units::header_only and will install in a llnl-units directory with appropriate cmake files.

If compiling as part of a subproject then a few other options are useful

  • UNITS_HEADER_ONLY: Only generate the header only target, sets UNITS_BUILD_STATIC_LIBRARY and UNITS_BUILD_SHARED_LIBRARY to OFF

  • UNITS_INSTALL: enable the install instructions of the library

  • UNITS_BUILD_OBJECT_LIBRARY: Generate an object library that can be used as part of other builds. Only one of UNITS_BUILD_SHARED_LIBRARY, UNITS_BUILD_STATIC_LIBRARY, or UNITS_BUILD_OBJECT_LIBRARY can be set to ON. If more than one are set, the shared library and object library settings take precedence over the static library.

  • UNITS_LIBRARY_EXPORT_COMMAND: If desired the targets for the units library can be merged into an root project target list by modifying this variable. The use cases for this are rare, but if this is something you want to do this variable should be set to something like EXPORT rootProjectTargets. It defaults to “EXPORT unitsTargets”

CMake Targets

If you are using the library as a submodule or importing the package there are a couple targets that can be used depending on the build. NOTE: these can be changed using UNITS_CMAKE_PROJECT_NAME.

  • units::units will be set to the library being built, either the shared, static, or object

  • units::header_only is a target for the headers if UNITS_HEADER_ONLY CMake variable is set, then only this target is generated. This target is always created.


As part of the HELICS library the units library is used as a submodule it is included by the following code

# so units cpp exports to the correct target export

     set(CMAKE_CXX_STANDARD 17) # Supported values are ``11``, ``14``, and ``17``.


     "${PROJECT_SOURCE_DIR}/ThirdParty/units" "${PROJECT_BINARY_DIR}/ThirdParty/units"

set_target_properties(units PROPERTIES FOLDER Extern)


Then the target linked by

target_link_libraries(helics_common PUBLIC HELICS::utilities units::units)